Variable inductor employing spaced magnetic hubs



Jan. 4, 1966 c, os 3,227,980

VARIABLE INDUCTOR EMPLOYING SPACED MAGNETIC HUBS Filed Feb. 27, 1965 INVENTOR. [2727720 611530591 6i 4 4 w "TORNEYS United States Patent 3,227,980 VARIABLE INDUCTOR EMPLOYING SPACED MAGNETIC HUBS Immo C. Roser, Mount Prospect, Ill., assignor to TRW Inc., a corporation of Ohio Filed Feb. 27, 1963, Ser. No. 261,425 3 Claims. (Cl. 336136) The present invention relates to an improved coil asembly, and particularly to coil assemblies designed to operate in relatively low frequency ranges.

In the past, coil assemblies intended for this type of use frequently included cup and washer assemblies or two cup structures made of a magnetic material of high permeability. Such structures, however, required a substantial amount of ferrites in the circuit to achieve suitable operating characteristics. This immediately raised the cost of the coil assembly in view of the expensive nature of the ferrites used. Furthermore, the electrical performance characteristics were not always satisfactory because the coils had a tendency to cause a drift in frequency with changes of temperature and their Q factor was not as high as might be desired in such circuits.

The present invention provides an improved coil assembly having improved mechanical and electrical properties. The new structure makes it possible to use considerably smaller amounts of ferrite in the coil structure than have heretofore been used. What is more, the electrical performance characteristics are improved because the Q factor is increased and the structure of the present invention has self-compensating frequency drift correction.

An object of the present invention is to provide an improved coil assembly using smaller amounts of fer romagnetic material than have heretofore been commonly used in coil structures of this type.

Another object of the invention is to provide an improved coil assembly having means for providing adjustable permeability in the core through the simple device of adjusting the thickness of a non-magnetic spacer.

A further object of the invention is to provide an improved coil assembly having a high Q factor at low frequencies.

Still another object of the invention is to provide a coil assembly having a self-compensating frequency drift characteristic.

In accordance with the present invention, I provide a coil assembly including a supporting base, and a nonmagnetic tube, normally composed of plastic or the like, supported on the base. The improved core structure takes the form of a two piece bobbin composed of a pair of flanged hubs in coaxial alignment on the tube with the hub portions thereof in confronting relation. The flanged hubs are composed of magnetic material of high permeability such as a ferrite. A non-magnetic gap is provided between the two confronting ends of the hubs by inserting a non-magnetic spacer between the opposed ends, the thickness of the spacer providing a means for controlling the permeability of the core to reasonably close limits. The two piece bobbin and the spacer are adhesively secured to the support tube, thereby providing a compact unit considerably smaller in size and in ferrite content to comparable cores of previous coil structures.

It has been found that the novel core structure provides the coil assembly with a considerably higher Q factor than is common in coil assemblies designed for relatively low frequency application. Furthermore, the coil assembly has a self-compensating frequency drift characteristic. For example, at increased temperatures, the drift of the coil itself is in the negative direction. This tendency is compensated by the elongation of the form on which the coil is mounted due to thermal expansion, causing a displacement of the adjusting core located within the form, thereby causing a drift in the positive direction which tends to compensate for the drift of the coil.

A further description of the present invention will be made in conjunction with-the attached sheet of drawings which illustrates a preferred embodiment of the invention.

In the drawings:

FIGURE 1 is an exploded view with parts partly in elevation and partly in cross-section illustrating a typical assembly of a coil according to the present invention;

FIGURE 2 is a view partly in elevation and partly in cross-section of the assembled coil assembly enlarged considerably for purposes of clarity; and

FIGURE 3 is a cross-sectional view taken substantially along the line IIIIII of FIGURE 2.

As shown in the drawings:

In FIGURE 1, reference numeral 10 indicates generally a sub-assembly consisting of a non-conductive base 11 and a molded cap and tube assembly generally identified at reference numeral '12 in FIGURE 1. The base 11 has a plurality of external prongs 13 for attaching the coil assembly to external circuitry and the external prongs 13 are, in turn, formed with internal connectors 14 for connecting suitable conductors to the ends of the coil windings themselves.

The cap and tube assembly 12 is preferably molded in a single piece from a plastic material such as nylon. The cap and tube assembly 12 includes a pedestal portion 16 which is clamped to the base 11 by means of an undulating pressure spring 17.

The upper portion of the cap and tube assembly 12 consists of a relatively thin walled tube section 18 which provides the form for the coil proper.

One of the features of the present invention resides in the novel bobbin structure on which the coil is wound. As best illustrated in FIGURE 1, the bobbin consists of two flanged hubs 19 and 21 with a non-magnetic spacer 22 composed of nylon, Mylar or the like interposed therebetween. Each of the flanged hubs 19 and 21 consists of a cylindrical hub portion 23 and 24, respectively, and has integral annular flange portions 26 and 27, re spectively. The spacer 22 is in the form of a washer and the thickness of the spacer is preselected to provide the desired amount of permeability in the core. The flanged hubs 19 and 21 both consist of a material having a high permeability, such as a ferrite. The thickness of the spacer 22 may vary typically from about 0.005 to 0.020 inch. In assembly, the flanged hubs 19 and 21 together with the spacer 22 are placed over the tube 18 with which they have a reasonably tight fit. Then, adhesive is applied between the periphery of the tube 18 and the mating hubs and spacer 22 to provide a firm bond.

Additional ferromagnetic material is provided in the circuit by the inclusion of a cup 28 also composed of a high permeability material such as ferrite or the like, and having an aperture 29. The cup 28 is disposed in inverted relation over the bobbin consisting of the two flanged hubs 19 and 21, and the spacer 22, and the coil 31 which is wound about the bobbin. A ferromagnetic threaded core 32 slips through the aperture 29 in the cup 28 and is adjustably positionable within the tube 18 by the threads on the core to vary the reluctance of the magnetic path.

A metal can 33 is provided as a shield for the core assembly and encloses the entire assembly as best illustrated in FIGURE 2. The shield 33 has secured to it a pair of grounding lugs 34 and 36, the lugs having struck out ears 37 which extend through suitable slots provided in the shield 33 and are pressed against the outer wall of the shield 33 as illustrated in FIGURE 2. A resilient J cushioning washer 38 is interposed between the cup 28 and the inner top wall of the shield 33 to serve as a spacer.

With the coil assembly of the present invention, the same performance characteristics can be achieved with an amount of ferrite about one-half the amount required for previous structures which involved the use of cups and washers or two cups. Because the non-magnetic gap provided by the spacer 22 can be made fairly small, and because the amount of ferrite used is also very small, the frequency drift of the coil assembly due to temperature variations is reasonably low. The small package provided by the decreased amount of ferrite also provides the coil assembly with a high Q factor.

From the foregoing, it will be seen that the coil assembly of the present invention provides, in a small package, a highly efficient core structure which is economical to manufacture. It should also be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

I claim as my invention:

1. A variable inductor comprising a support, a nonmagnetic thermally expansible tube on said support, a magnetic bobbin structure received in snug fitting relation about said tube, said bobbin structure being composed of a pair of hubs each of which has a tubular body portion and an enlarged flange portion thereon, the hubs being aligned with the tubular body portions thereof in confronting relation, a non-magnetic, non-conductive spacer disposed between the confronting tubular body portions to provide a non-magnetic gap therebetween, a

coil disposed around the hubs and between the flange portions, and a ferromagnetic core member extending through said bobbin structure and being adjustably positionable within said tube.

2. A variable inductor comprising a support, a nonmagnetic thermally expansible tube on said support, a magnetic bobbin structure received in snug fitting relation about said tube, said bobbin structure being composed of a pair of hubs each of which has a tubular body portion and an enlarged flange portion thereon, the hubs being aligned with the tubular body portions thereof in confronting relation, a non-magnetic, non-conductive spacer disposed between the confronting tubular body portions to provide a non-magnetic gap therebetween, a coil disposed around the hubs and between the flange portions, a ferromagnetic cup disposed in inverted relation over said bobbin structure, and a ferromagnetic core member extending through said bobbin structure and being adjustably positionable within said tube.

3. The variable inductor of claim 1 in which said tubular body portion of said hub and said spacer are adhesively secured to said tube.

References Cited by the Examiner UNITED STATES PATENTS 2,628,342 2/1953 Taylor 33683 X 2,630,560 3/1953 Earl et a1 336136 X 2,648,031 8/1953 Lang et al 336-136 X JOHN F. BURNS, Primary Examiner. 

1. A VARIABLE INDUCTOR COMPRISING A SUPPORT, A NONMAGNETIC THERMALLY EXPANSIBLE TUBE ON SAID SUPPORT, A MAGNETIC BOBBIN STRUCTURE RECEIVED IN SNUG FITTING RELATION ABOUT SAID TUBE, SAID BOBBIN STRUCTURE BEING COMPOSED OF A PAIR OF HUBS EACH OF WHICH HAS A TUBULAR BODY PORTION AND AN ENLARGED FLANGE PORTION THEREON, THE HUBS BEING ALIGNED WITH THE TUBULAR BODY PORTIONS THEREOF IN CONFRONTING RELATION, A NON-MAGNETIC, NON-CONDUCTIVE SPACER DISPOSED BETWEEN THE CONFRONTING TUBULAR BODY PORTIONS TO PROVIDE A NON-MAGNETIC GAP THEREBETWEEN, A COIL DISPOSED AROUND THE HUBS AND BETWEEN THE FLANGE PORTIONS, AND A FERROMAGNETIC CORE MEMBER EXTENDING THROUGH SAID BOBBIN STRUCTURE AND BEING ADJUSTABLY POSITIONABLE WITHIN SAID TUBE. 